Magnetic centrifugal switch

ABSTRACT

Centrifugal switching device having a magnet rotating with a shaft and an armature attracted by the magnet. The armature also rotates with the shaft and is pivoted so as to operate a switch when the centrifugal force is great enough to free the armature from the magnet. Adjustable nuts are provided to allow for a variation of the operating radius of the mass of the armature.

United States Patent Inventor Peter B. Smhh Monroe, Conn.

Appl. No. 843,404

Filed July 22, 1969 Patented Sept. 7, 1971 Assignee Dynamics Corporation of America New York, N.Y.

MAGNETIC CENTRIFUGAL SWITCH 8 Claims, 4 Drawing Figs.

Int. H01h 35/10 Field of Search 200/80;

[56] References Cited UNITED STATES PATENTS 2,446,923 8/1948 Hardy 200/80 3,129,301 4/ 1964 Saphra 200/80 Primary Examiner- Herman J. Hohauser Attorne'y- Richard Schulze PATENTED SEP 7 ISYI SHEET 1 (IF 2 R m v m PETE R B. SMITH PATENTEUSEP m 3603.751

sniff '2 or 2 Comrifigol Fofco mvsm'on PETER a. swarm ROTATIONAL SPEED MAGNETIC CENTRIFUGAL SWITCH This invention relates generally to centrifugal switches and more particularly to magnetic centrifugal switches.

The normal method of operation for a centrifugal type of switch is to provide a pair of flyballs held down by springs which, when acted upon by centrifugal force to an extent necessary to overcome the bias of the springs, will move outwardly and thereby actuate the switch. One of the major problems of this type of switch results from the fact that the springs form part of the switching action and the whole switch is subject to set point variation due to external vibrations acting on the springs.

This set point variation is particularly true when such switches are used on internal combustion engines. Under certain load and speed conditions, various torsional vibrations occur. These torsional vibrations can excite the springs at their natural frequency which effectively changes the spring rate and hence the retaining force exerted by the springs. Such a change drastically affects the set point of the switch. Because of the heavy masses involved in this kind of switch, wear occurs at pivot and fulcrum points which in turn changes the set point.

A number of switches have been developed which employ some type of magnetic attraction to hold a switch closed until such attraction is overcome by centrifugal force from means such as weights attached to a shaft. However, all such devices, to the best of my knowledge, are manufactured with a fixed point at which the switch will open and are not readily variable for different operations by the user.

Accordingly, it is an object of this invention to provide a centrifugal switch which uses no restraining springs for biasing against centrifugal force.

Another object of this invention is to provide a centrifugal switch wherein a magnet is used as a restraining means for biasing against centrifugal force and includes means for varying the operating radius of the mass of the armature.

These and other objects of the invention will become apparent from the following description when taken in conjunction with the drawings wherein:

FIG. 1 is a sectional view of the switching device of the present invention;

FIG. 2 is a fragmentary view of the magnet and armature used in FIG. 1;

FIG. 3 is a partial sectional view of the details of the centrifugal mechanism of FIG. 1; and

FIG. 4 is a graphic illustration relating centrifugal and magnetic forces to the rotational speed of the shaft on which the switch is mounted.

Turning now more specifically to the drawings, there is shown in FIG. 1 a switch housing 11 enclosing the shaft 13 which extends through the housing 11 and is rotatably secured therein by means of bearings 15 and 17.

A magnet 19 is secured to and rotatable with shaft 13. Magnet 19 is of the sandwich type and includes pole pieces 21 and These pole pieces are preferably flattened such as at 25 for reasons which will become apparent as the description proceeds.

Armatures 27 and 29 are pivotally secured to plate 31 at pivot points 33 and 35. Mounted at the outer ends of the armatures 27 and 29 are rocker arms 37 and 39 which are of a U-shaped channel configuration, as is more clearly shown in FIG. 2, and which are pivotally mounted to the armature at pivot points 38 and 40 and pass therethrough. Again as shown in FIG. 2, the open edges of the rocker arms make the actual abutting contact with the pole pieces 21 and 23 of magnet 19. This configuration assures a positive and even contact across the pole pieces.

Plate 31 is secured to a male cup member 49 which slidably extends within the female cup member 51 and is biased outwardly therefrom by means of a light spring 53. Plate 31 and cup members 49 and 51 are all secured to and rotate with shaft 13.

Microswitches 69 and 71 are actuated by means of switch arms 65 and 67, respectively. These arms terminate in rolling contacts 66 and 68 which are contacted by the back face of the male cup member 49.

Threaded bolts 55 and 57 are secured to the outer faces of rocker arms 37 and 39 respectively by means such as welding. Each bolt has a rotatable nut 59, 61 associated therewith for purposes which will become apparent as the description proceeds.

Turning now to FIG. 3, there is illustrated the operation of the switch arms as previously described in FIGS. 1 and 2.

It will be appreciated that any number of switch arms could be used with this type of magnetic switch although only two have been illustrated for descriptive purposes. It is understood that if more than one switch is used, it would be for purposes of operating separate control functions at different speeds of rotation of the shaft.

As the shaft reaches the particular speed at which one switch, such as switch 71, is to be operated, the armature 29 develops enough centrifugal force to overcome the attraction of the magnet 19 and the armature moves outwardly to the dotted line position shown in FIG. 3. This in turn moves the male cup member 49 into the female cup member 51 to the- I dotted line position indicated as 73 and causes the switch arm 67 to move to its dotted line position which actuates switch 71. A stop member 43 is mounted on plate 31 to prevent the armature 29 from exceeding the predetermined limits.

As the speed of the motor further increases, the operating point for the armature 27 is reached and it passes outwardly to the position shown in the dotted line which further extends the male cup member 49 into the female cup member 51 and contacts the roller 66 of switch arm 65 moving it to its dotted line position and actuating switch 69.

In order to obtain a fine adjustment of the operating points for the armatures, screws 55 and 57 may be mounted on the rocker arms 37 and 39. Adjustable nuts 59 and 61 may be run up and down the screw to the position desired and a grommet 63 may be provided in the housing 11 for access to the adjustable nuts. The principle of operation is as follows.

The operation of the switch is dependent on the fact that at a given speed, the centrifugal force imposed on the mass of the armature becomes equal to and subsequently greater than the restraining force caused by the magnetic attraction between the armature and the magnet. As shown in FIG. 4, the magnetic attraction depicted by line is constant until such time as the armature leaves the magnet, at which time the magnetic force decreases as the square of the distance between the armature and the magnet (air gap).

The centrifugal force shown as line 82, increases proportionally to the rotating speed, assuming mass and operating radius of the mass to be constant. At the point shown as X" in FIG. 4, where the increasing centrifugal force becomes greater than the fixed magnetic force, the armature starts to leave the magnet. At this point, there are two changes which occur in the forces between the armature and magnet. 1. As the armature leaves the magnet, its mass moving outwards operates at a larger radius (original radius plus air gap). Thus,

the centrifugal force is increasing as the air gap becomes greater. 2. The magnetic force holding the armature to the magnet is decreasing as the square of the air gap distance.

Therefore, we have an outward force increasing proportionally to the operating radius of its mass and an inwa'rd force decreasing by the square of the air gap which causes a true snap action. The point of separation, point X, may be moved along the speed axis by varying the operating radius of the mass of the armature. This is achieved by repositioning the nuts 59 and 61 which form a part of such mass. With the nuts positioned as shown in FIG. 3, armature 29 will move to its dotted line position at a lower rotation speed than will armature 27 since nut 61 is at the extreme outer end of threaded bolt 57.

The nuts 59 and 61 are easily adjustable by access to the interior of the switch when grommet 63 is removed.

It will be obvious from the above description and drawings that a switch has been provided which eliminates the normal springs used in centrifugal switches and, therefore, makes it insensitive to torsional vibrations particularly as used with engines and the like. Further, there has been provided a means for manually adjusting the points of operation of the switches relative to the rotational speed of the shaft. Further tests have shown a set point repeatability of better than 3 r.p.m. when set for 2000 r.p.m.

lt is to be understood that the above description and drawings are illustrative only and that equivalent parts may be substituted in the basic device without departing from the scope of the invention.

I claim:

1. A switching device responsive to shaft rotational speed comprising a magnet mounted on and rotatable with said shaft,

at least one armature having one end held by the attractive force of said magnet,

means for pivotally mounting said armature adjacent said shaft and rotatable therewith,

switch means operated by said armature when said armature is moved away from said magnet by centrifugal force, and

adjustable means varying the point at which centrifugal force will separate said armature away from said magnet.

2. The device of claim 1 further comprising pole pieces on said magnet, said pole pieces having at least one flat edge for contact with said armature. 3. The device of claim 2 further comprising a rocker arm mounted on said one end of said armature for contacting said flat edges of said pole pieces. 4. The device of claim 1 wherein said adjustable means comprises a threaded bolt mounted on said armature and extending outwardly from said magnet, and a rotatable nut adjustable to predetermined positions on said bolt. 5. The device of claim 1 further comprising a second armature having adjustable means and magnetically attracted to and rotatable with said magnet, said second armature being adjusted so as to separate from said magnet at a different predetermined centrifugal force than said other armature, and a second switch coupled to said second armature and activated thereby. 6. The device of claim 5 wherein the adjustable means for each of said armatures comprises a threaded bolt mounted on each of said armatures, and a rotatable nut adjustable to predetennined positions on each of said bolts. 7. The device of claim 1 wherein the adjustable means comprises screw threaded means carried by said armature.

8. The device of claim 5 wherein the adjustable means comprise screw threaded means carried by each of said armatures. 

1. A switching device responsive to shaft rotational speed comprising a magnet mounted on and rotatable with said shaft, at least one armature having one end held by the attractive force of said magnet, means for pivotally mounting said armature adjacent said shaft and rotatable therewith, switch means operated by said armature when said armature is moved away from said magnet by centrifugal force, and adjustable means varying the point at which centrifugal force will separate said armature away from said magnet.
 2. The device of claim 1 further comprising pole pieces on said magnet, said pole pieces having at least one flat edge for contact with said armature.
 3. The device of claim 2 further comprising a rocker arm mounted on said one end of said armature for contacting said flat edges of said pole pieces.
 4. The device of claim 1 wherein said adjustable means comprises a threaded bolt mounted on said armature and extending outwardly from said magnet, and a rotatable nut adjustable to predetermined positions on said bolt.
 5. The device of claim 1 further comprising a second armature having adjustable means and magnetically attracted to and rotatable with said magnet, said second armature being adjusted so as to separate from said magnet at a different predetermined centrifugal force than said other armature, and a second switch coupled to said second armature and activated thereby.
 6. The device of claim 5 wherein the adjustable means for each of said armatures comprises a threaded bolt mounted on each of said armatures, and a rotatable nut adjustable to predetermined positions on each of said bolts.
 7. The device of claim 1 wherein the adjustable means comprises screw threaded means carried by said armature.
 8. The device of claim 5 wherein the adjustable means comprise screw threaded means carried by each of said armatures. 